Download 18. Figure 18.1

Figure 18.1. Influence of soil organic matter and its management on nutrient availability.
Growth-promoting substances
A
B
residue
C
During the decomposition process,
growth-promoting substances are
produced (A), soil structure is improved
and water holding capacity is increased
(B), nutrients are mineralized (during C,
D, and E), and CEC is produced (C, D,
and E).
D
Direct Effects on Nutrient Availability
1) Nutrients released during residue decomposition.
Relatively high amounts of mineralization of available
nutrients are produced by a combination of rapid
decomposition plus previously accumulated POM or a high
amount of added residues. Rapid decomposition is stimulated
by intensive tillage, good soil drainage, coarse texture, and
alternating wet and dry conditions.
2) CEC produced during decomposition process.
Better soil structure and improved waterholding capacity
Active organic matter
(particulate, light fraction)
E
Passive organic matter
(humus, organo-mineral complexes)
Indirect Effects on Nutrient Availability
1) Growth-promoting substances. Substances produced
by bacteria promote better root growth and healthier roots and
lead to the exploration of more soil volume and more surface
area for nutrient interception and mass flow of nutrients to
roots.
2) Better soil structure and improved water-holding
capacity. Better soil structure may enhance root
development and exploration (see above). Good soil structure
and plentiful humus content contribute to higher amounts of
plant-available water following rains or irrigation. This
results in better plant growth and health and more nutrient
movement to roots.